I always have trouble making sense of the schematic on 6803 games, but if I'm interpreting it correctly, it looks like you could try unplugging J6 on the mpu board, that's the ground path for all the red-wire coils (though the schematic references a "solenoid expander" close by that appears to connect to that red-wire 43v circuit when the expander is activated...not sure where the expander is located or how it works exactly)
It's not uncommon for a shorted transistor on the mpu to lock on a coil and blow the fuse. Hopefully by disconnecting J6 and replacing the fuse, you'll find the fuse doesn't blow. If the fuse doesn't blow, you'll need to figure out which of the coils leading to J6 is locking on due to a bad transistor/chip/diode/shorted coil or wiring etc.
Schematic is a little blurry when i zoom in on my phone, but here's the area of the schematic i was looking at, from section 2-18:
Screenshot_20190304_113811_com.google.android.apps.docs(1).jpg